Buggy code:
public class EditProductUI { JFrame frame ; static Connection connection = null ; private static JTextField productTextField ; private static JTextField areaTextField ; private static JTextField kilosTextField ; private static JTextField priceTextField ; private static JTextField newKiloTextField ; private static JTextField newPriceTextField ; public static int kilos ; public static int price ; public EditProductUI ( ) { } public void updateKilos ( ) { } public void updatePrice ( ) { } private void initialize ( ) { frame = new JFrame ( ) ; frame . setTitle ( "Επεξεργασία<seq2seq4repair_space>Προϊόντος" ) ; frame . setResizable ( false ) ; frame . setBounds ( 100 , 100 , 506 , 405 ) ; frame . setDefaultCloseOperation ( JFrame . DISPOSE_ON_CLOSE ) ; JPanel panel = new JPanel ( ) ; frame . getContentPane ( ) . add ( panel , BorderLayout . CENTER ) ; JLabel productLabel = new JLabel ( "Προιόν:" ) ; JLabel countyLabel = new JLabel ( "Νομός:" ) ; JLabel kiloLabel = new JLabel ( "Κιλά:" ) ; JLabel priceLabel = new JLabel ( "Τιμή:" ) ; EditProductUI . productTextField = new JTextField ( ) ; EditProductUI . productTextField . setEditable ( false ) ; EditProductUI . productTextField . setColumns ( 10 ) ; EditProductUI . productTextField . setText ( product ) ; EditProductUI . areaTextField = new JTextField ( ) ; EditProductUI . areaTextField . setEditable ( false ) ; EditProductUI . areaTextField . setColumns ( 10 ) ; EditProductUI . areaTextField . setText ( area ) ; EditProductUI . kilosTextField = new JTextField ( ) ; EditProductUI . kilosTextField . setEditable ( false ) ; EditProductUI . kilosTextField . setColumns ( 10 ) ; EditProductUI . kilosTextField . setText ( String . valueOf ( ViewProducerProductsUI . kilos ) ) ; EditProductUI . priceTextField = new JTextField ( ) ; EditProductUI . priceTextField . setEditable ( false ) ; EditProductUI . priceTextField . setColumns ( 10 ) ; EditProductUI . priceTextField . setText ( String . valueOf ( ViewProducerProductsUI . price ) ) ; JLabel lblNewLabel_4 = new JLabel ( "Εισαγωγή<seq2seq4repair_space>Νέων<seq2seq4repair_space>Κιλών:" ) ; EditProductUI . newKiloTextField = new JTextField ( ) ; EditProductUI . newKiloTextField . setColumns ( 10 ) ; JLabel lblNewLabel_5 = new JLabel ( "Εισαγωγή<seq2seq4repair_space>Νέας<seq2seq4repair_space>Τιμής:" ) ; EditProductUI . newPriceTextField = new JTextField ( ) ; EditProductUI . newPriceTextField . setColumns ( 10 ) ; JButton changeButton = new JButton ( "Αλλαγή" ) ; changeButton . addActionListener ( new ActionListener ( ) { public void actionPerformed ( ActionEvent arg0 ) { if ( SearchFormController . isNull ( EditProductUI . newKiloTextField . getText ( ) ) ) { System . out . println ( "DO<seq2seq4repair_space>NOTHING" ) ; } else if ( ( SearchFormController . isInteger ( EditProductUI . newKiloTextField . getText ( ) ) ) && ( SearchFormController . isPositive ( EditProductUI . newKiloTextField . getText ( ) ) ) ) { updateKilos ( ) ; JOptionPane . showMessageDialog ( null , "Ç<seq2seq4repair_space>áëëáãÞ<seq2seq4repair_space>ôùí<seq2seq4repair_space>êéëþí<seq2seq4repair_space>Ýãéíå<seq2seq4repair_space>ìå<seq2seq4repair_space>åðéôõ÷ßá." , "ÓöÜëìá" , JOptionPane . INFORMATION_MESSAGE ) ; } else JOptionPane . showMessageDialog ( null , "Ôï<seq2seq4repair_space>ðåäßï<seq2seq4repair_space>'ÅéóáãùãÞ<seq2seq4repair_space>ÍÝùí<seq2seq4repair_space>Êéëþí'<seq2seq4repair_space>äÝ÷åôå<seq2seq4repair_space>ìüíï<seq2seq4repair_space>èåôéêïýò<seq2seq4repair_space>áñéèìïýò" , "ÓöÜëìá" , JOptionPane . ERROR_MESSAGE ) ; if ( SearchFormController . isNull ( EditProductUI . newPriceTextField . getText ( ) ) ) { System . out . println ( "DO<seq2seq4repair_space>NOTHING" ) ; } else <START_BUG> if ( ( SearchFormController . isInteger ( EditProductUI . newPriceTextField . getText ( ) ) ) && ( SearchFormController . isPositive ( EditProductUI . newPriceTextField . getText ( ) ) ) ) { <END_BUG> updatePrice ( ) ; JOptionPane . showMessageDialog ( null , "Ç<seq2seq4repair_space>áëëáãÞ<seq2seq4repair_space>ôçò<seq2seq4repair_space>ôéìÞò<seq2seq4repair_space>Ýãéíå<seq2seq4repair_space>ìå<seq2seq4repair_space>åðéôõ÷ßá." , "ÓöÜëìá" , JOptionPane . INFORMATION_MESSAGE ) ; } else JOptionPane . showMessageDialog ( null , "Ôï<seq2seq4repair_space>ðåäßï<seq2seq4repair_space>'ÅéóáãùãÞ<seq2seq4repair_space>ÍÝáò<seq2seq4repair_space>ÔéìÞò'<seq2seq4repair_space>äÝ÷åôå<seq2seq4repair_space>ìüíï<seq2seq4repair_space>áñéèìïýò" , "ÓöÜëìá" , JOptionPane . ERROR_MESSAGE ) ; frame . dispose ( ) ; ViewProducerProductsUI viewMyProducts = null ; try { viewMyProducts = new ViewProducerProductsUI ( ) ; } catch ( SQLException e ) { e . printStackTrace ( ) ; } viewMyProducts . frame . setVisible ( true ) ; } } ) ; JSeparator separator = new JSeparator ( ) ; JButton button = new JButton ( "Πίσω" ) ; button . addActionListener ( new ActionListener ( ) { public void actionPerformed ( ActionEvent arg0 ) { frame . dispose ( ) ; ViewProducerProductsUI viewProducerProductsUI = null ; try { viewProducerProductsUI = new ViewProducerProductsUI ( ) ; } catch ( SQLException e ) { e . printStackTrace ( ) ; } viewProducerProductsUI . frame . setVisible ( true ) ; } } ) ; GroupLayout gl_panel = new GroupLayout ( panel ) ;

Fix:
if ( ( SearchFormController . isNumeric ( EditProductUI . newPriceTextField . getText ( ) ) ) && ( SearchFormController . isPositive ( EditProductUI . newPriceTextField . getText ( ) ) ) ) {